In the field of medical technology, there are various known pieces of apparatus by which liquids can be withdrawn from patients or liquids can be fed to the patients via a flexible line. In this case, access is generally gained to the patients by means of a catheter for insertion in organs of the body or a needle for puncturing vessels. During the examination or treatment, it has to be ensured that the access remains in proper order. It is therefore necessary for the patient access to be monitored.
A proper access to the patient is a prerequisite, in particular, for extracorporeal blood treatment devices that comprise an extracorporeal blood circuit. The known pieces of apparatus for extracorporeal blood treatment include for example dialysis apparatus and cell separators, both of which require access to the patient's vascular system. In extracorporeal blood treatment, blood is withdrawn from the patient via a flexible arterial line having an arterial puncturing needle and is fed back to the patient via a flexible venous line having a venous puncturing needle.
Despite the vascular access being monitored regularly by the hospital staff there is, basically, a risk of the puncturing needle slipping out of the patient's blood vessel unnoticed. The risk of the puncturing needle slipping out unnoticed also exists with home dialysis. Various arrangements of different designs for monitoring the vascular access are known. The known monitoring arrangements generally rely on the safety arrangements which are provided as standard in the pieces of blood-treating apparatus and which shut off the extracorporeal blood circuit immediately if there is anything wrong with the vascular access.
There are known arrangements for monitoring a vascular access which have a device for detecting moisture to enable blood escaping at the point of puncture to be detected. The known devices for detecting moisture which are used in the known monitoring arrangements for the patient access take the form of pads to be applied to the point of puncture. The pad is composed of an absorbent material in which a sensor of liquid is embedded.
WO 2006/008866 A1 and U.S. Pat. No. 6,445,304 B1 for example describe devices for detecting moisture which are made of an absorbent material which is applied to the skin. The known pads are characterized by the fact that the sensor of liquid is embedded in the absorbent material.
The sensor of liquid in WO 2006/008866 A1 has two printed conductors which are applied to a substrate material. At one end, the two printed conductors take the form of connecting contacts while at the other end the printed conductors are electrically connected to a terminating resistor. The printed conductors and the terminating resistor are printed on the substrate material. Conductive ink is used for this purpose.
Whereas the printed conductors can be printed on the substrate material with relatively little production-related cost or complication, the production of a printed terminating resistor having a defined resistance which is to be within relatively tight tolerances is found to be relatively problematic. On the one hand it has proved that printed terminating resistors may be subject to relatively wide production-related tolerances. On the other hand it has been seen that the alternating bending strength of terminating resistors printed on a substrate material may be relatively low. This is a problem inasmuch as the terminating resistor is constantly stressed in bending when there are movements on the part of the patient.
The printing of the printed conductors on the substrate material, such for example as a nonwoven material, may be performed in a first printing operation with a silver-containing paste which is dried after the printing operation. In a second printing operation, the terminating resistor can be printed on the substrate material with high-resistance graphite paste. Different forms for the ends of the printed conductors and the terminating resistor are possible in this case.
In a first design, the space on the substrate material which is situated between two ends, which extend parallel to one another, of the printed conductors has a high-resistance graphite paste printed on it. The spacing between the parallel ends of the printed conductors is approximately 1 mm in this case. With this design, it has already been found that even a +/−10% variation in the spacing between the ends of the printed conductors may result in the value of the resistance of the terminating resistor varying by +/−50%. Variations of this kind in the spacing between the ends of the printed conductors may occur due to shrinkage processes in the course of drying or even due to mechanical stresses on the substrate material in practical use such for example as when there are movements on the part of the patient or when a protective film is pulled off the substrate material. A further disadvantage of this design lies in the fact that a small drop of liquid situated on the terminating resistor itself cannot be detected.
In an alternative design, the terminating resistor is not printed on the space situated between two parallel ends of printed conductors and instead the terminating resistor which is printed on the substrate material in a high-resistance paste is in the form of a U whose two sides are connected to the two ends of the printed conductors, i.e. the two ends of the printed conductors continue into the sides of the U-shaped terminating resistor with their width unchanged. The ends of the sides of the U-shaped terminating resistor overlap the two ends of the printed conductors in this case. With this design, it has been found that the variation in the value of the resistance of the terminating resistor can be reduced to +/−30%, and it is not a matter of direct importance for a given spacing to be maintained between the ends of the printed conductors.
Even though lower tolerances can be achieved for the terminating resistor with the alternative design, there are found to be problems in practice in obtaining a repeatable terminating resistor which is printed on the substrate material.
A further disadvantage of printed terminating resistors lies in the fact that sweat from the patient may reduce the value of the resistance of the terminating resistor. Also, there are more stringent requirements set for the biocompatibility of the printed terminating resistor because the terminating resistor may come into contact with the patient's skin.
A further disadvantage of a printed terminating resistor arises from the requirement for a number of moisture sensors which is as large as possible to be arranged on a single printed sheet. The size of the sheets for printing (sheets of nonwoven material) which can be inserted in the printing machine is limited due to the accuracy requirements imposed by the printing when, once the printed conductors printed with the silver-containing paste in the first printing operation have dried, the terminating resistors are to be printed in the graphite paste, in the second printing operation, on the same printed sheet in an exact position next to the printed conductors. Because of the shrinkage of the sheet when the first printing dries, a non-uniform displacement occurs of the second printing relative to the first printing and this increases as the size of the sheets becomes larger and as from a certain sheet size can no longer be accepted because at least some of the terminating resistors are then no longer accurately positioned in the second printing operation. However, for reasons of cost, an attempt has to be made to use sheets which are as large as possible carrying as many individual sensors as possible, because the specific costs of an individual sensor go down as the size of the printed sheet increases. In conflict with this, there is a desire to be able to use moisture sensors, having a terminating resistor, which can be printed particularly inexpensively.
An object underlying the present invention is to provide, for use with an arrangement for monitoring an access to a patient, a device for detecting moisture which can be produced without any great production-related cost or complication, which will reliably withstand the mechanical stresses due, for example, to movements on the part of the patient, which will give repeatable measured results and which has high biocompatibility.
As well as this, an object underlying the present invention is also to provide an arrangement for monitoring an access to a patient, and in particular for monitoring the vascular access in extracorporeal blood treatment, which calls for relatively little production-related cost or complication, which reliably withstands the mechanical stresses due, for example, to movements on the part of the patient, which gives repeatable measured results and which has high biocompatibility. It is also an object of the present invention to provide an apparatus for extracorporeal blood treatment which has an arrangement of this kind for monitoring the vascular access.
The device according to the present invention for detecting moisture takes the form of a covering (pad) to be applied to the patient's skin which has a flexible substrate material to which an electrically conductive structure comprising printed conductors is applied as a moisture sensor. As the electrically conductive structure is applied, or preferably printed, on to a flexible substrate, the electrically conductive structure is not a component of the substrate.
The device for detecting moisture is characterized in that the electrically conductive structure has two printed conductors, with one end of the first printed conductor and one end of the second printed conductor having a first pair of connecting contacts and the other end of the first printed conductor and the other end of the second printed conductor having a second pair of connecting contacts. The first pair of connecting contacts serves to connect to the arrangement for monitoring the vascular access whereas the second pair of connecting contacts serves to connect to the terminating resistor. Because the terminating resistor is not part of the device for detecting moisture, the device can be inexpensively produced in large quantities.
The connecting contacts are preferably formed from the ends of the printed conductors, i.e. it is preferable for the ends or end sections of the printed conductors to be formed as connecting contacts. In this case it is preferable for the connecting contacts to lie on one side of the pad.
Whereas the device for detecting moisture is generally intended to be used only once, the terminating resistor, being a separate component, can be reused repeatedly after a cleaning operation which may possibly be necessary.
Because there is not a terminating resistor present on the flexible substrate material but one is provided separately, there is no risk that the terminating resistor might be damaged due to movements on the part of the patient. What is more, there is also no risk of the resistance of the terminating resistor being able to change as a result of alternating bending stresses due to movements on the part of the patient.
Because the terminating resistor does not come into contact with the patient's skin in practice, there is no necessity for the terminating resistor to be produced from a biocompatible material and there is no risk that sweat from the patient might reduce the value of the resistance of the terminating resistor.
What may be used as a terminating resistor is a conventional resistor which does not have to be applied to the flexible substrate material. Resistors which meet tight tolerances are available at low cost. The terminating resistor may for example be an SMD resistor (miniature resistor). The tolerance on the value of the resistance of such resistors is generally only +/−1%. Even should the SMD resistor come into contact with the patient's skin, the SMD resistor has better biocompatibility than a directly printed resistor.
With the two printed conductors, the terminating resistor makes it easier for the device for detecting moisture to be checked for serviceability by making a measurement of the resistance between the first pair of connecting contacts. If the moisture sensor is serviceable, the resistance measured between the connecting contacts will be the sum of the resistance of the terminating resistor and the resistances of the two printed conductors.
The use of separate terminating resistors has the advantage that a large number of individual sensors can be arranged on one printed sheet, because the shrinkage of the printed sheet is immaterial to the accurate positioning of the terminating resistor when this resistor is external. Also, the printing operation for applying the terminating resistors is dispensed with, thus saving production costs for the printing.
The device for detecting moisture may be designed to take different forms. It may not only be used in blood-treating apparatus which create a vascular access by means of a needle or catheter but is also basically suitable for use in other apparatus. Consequently, the device according to the present invention for detecting moisture is not confined to use in arrangements for monitoring an access to a patient.
A further possible area of application for the device according to the present invention for detecting moisture is for example the monitoring of connectors in medical technology, such for example as Luer connectors or Luer lock connectors. Connectors of this kind comprise a male and a female part of the connector which can be connected together with an air-tight and liquid-tight seal. Leaks may occur if the connectors are not properly connected. Luer connectors and Luer lock connectors are found for example on the system of flexible lines of an extracorporeal blood circuit. In this case the connectors may be monitored by the device according to the present invention to allow a blood loss due to a leak to be detected.
For monitoring leaks from Luer or Luer lock connectors, the device for detecting moisture (the pad) should be of a special design. For this application, the outside dimensions of the pad should be of a size such that the connector or connectors to be monitored can be wrapped as completely as possible in the pad. When the connector is being wrapped, that side of the sensor on which the printed conductors are printed should be directed inwards so that any liquid escaping from the connector can make its way straight onto the printed conductors. Means for fastening the pad to the connector and/or to the flexible line connected to the connector may be provided on the pad and/or the connector and/or on the flexible line. Means for sticking the pad firmly to the connector and/or the flexible line, such for example as adhesive strips, are preferably provided.
The two printed conductors which lead to the connecting contacts may be of different forms. They may each comprise a plurality of portions which are connected together electrically. All that is crucial is that the ends of the printed conductors have connecting contacts to enable on the one hand the monitoring arrangement and on the other hand the terminating resistor to be connected.
Basically, the two printed conductors may follow any desired path on the substrate material. However, to increase sensitivity, they should, as far as possible, be arranged to lie next to one another on the substrate material for their entire length. The entire area available on the substrate material should, as far as possible, be used in this case.
A preferred embodiment makes provision for the first and second pairs of connecting contacts to be arranged on a connecting member belonging to the covering. In this way, all the connecting contacts are easily accessible from one side. The connecting contacts are preferably arranged to be situated next to one another on the connecting member, thus enabling contact to be made with them easily.
In a further preferred embodiment, the two printed conductors each have two portions, with those ends of the two portions which are to be connected together of each printed conductor each being arranged on the connecting member. This embodiment allows the portions of the printed conductors to be electrically connected at the connecting member. The fact of the ends of the printed conductors being run back to the connecting member makes it possible to avoid crossing points at which otherwise the printed conductors would have to cross over one another but without, in so doing, coming into contact with one another. Crossing points of this kind cannot be avoided in printed circuits or can only be avoided at high cost.
An embodiment which is a particular preference provides four pairs of connecting contacts, with two pairs of connecting contacts serving to connect to the arrangement for monitoring the vascular access and to the terminating resistor and two pairs of connecting contacts serving to electrically connect the portions of the printed conductors.
The printed conductors are preferably printed on the substrate material by the screen printing process. The substrate material is preferably a nonwoven material on which the printed conductors can be printed. In the case of a water-based printing ink for example, the surface of the nonwoven material should not be hydrophobic. The nonwoven material also has to be capable of withstanding the stress necessary for the drying of the printing ink, from, for example, heat or UV radiation.
The covering is preferably a U-shaped form but may equally as well be rectangular, circular or oval. The U-shaped covering allows the needle for the patient access to rest on the patient's skin both before and after the covering is applied. However, instead of the covering being U-shaped, it is also possible for an opening for the needle to be passed through to be provided in the covering. However, the needle can then only be inserted once the covering has been applied.
In a further and particularly preferred embodiment, the covering has one or more cut-outs which, together with suitably formed projections on a connecting part of the arrangement for monitoring the patient access which is to be connected to the covering, serve to align the covering and fix it in position.
The arrangement according to the present invention for monitoring an access to a patient, and in particular for monitoring the vascular access in the case of an extracorporeal blood treatment, has the device according to the present invention for detecting moisture. The arrangement for monitoring the patient access preferably has an analyzing unit able to be connected to the device for detecting moisture which, if moisture is detected, triggers an audio and/or visual and/or tactile alarm. A control signal may also be generated to act on the control system of the apparatus by which, via the flexible line, a liquid is being fed to the patient and/or a liquid is being withdrawn from the patient.
The monitoring arrangement preferably has a connecting part, to which the device for detecting moisture is connected to make an electrical connection between the analyzing unit of the monitoring arrangement and the moisture sensor of the device for detecting moisture. The connecting part of the monitoring arrangement is preferably electrically connected to the analyzing unit by a connecting cable of adequate length. Alternatively, it is however also possible for a wireless connection to be made.
In a preferred embodiment the connecting part has a first and a second pair of connecting contacts to which the first and second pair of connecting contacts of the device for detecting moisture can be connected. The first pair of connecting contacts have a connecting cable for making an electrical connection between the analyzing unit of the monitoring arrangement and the moisture sensor of the device for detecting moisture, whereas the second pair of connecting contacts are connected together electrically by the terminating resistor. In this embodiment, the terminating resistor is part of the connecting part of the connecting cable of the monitoring arrangement. It is however possible for the terminating resistor to be provided not in the connecting part of the monitoring arrangement but in the monitoring arrangement, in particular in the analyzing unit. A four-core connecting cable then has to be used, with two cores being intended for the moisture sensor and two cores for the terminating resistor. The terminating resistor can also be provided on the connecting cable or be an integral part of the connecting cable. In this case the terminating resistor can be connected to the connecting cable at any point. A further alternative embodiment provides for a connecting cable having a connecting part with which the connecting cable can be connected to the monitoring arrangement. In this alternative embodiment the terminating resistor may be a component of the connecting part of the connecting cable to be connected to the monitoring arrangement.
The terminating resistor is preferably a miniature resistor (SMD resistor) which can easily be incorporated in the connecting part. SMD resistors have tight tolerances as components and are inexpensive.
The order of the connecting contacts on the connecting part may be as desired. The only thing that is important is that two connecting contacts can be electrically connected to the analyzing unit and two connecting contacts can be electrically connected to the terminating resistor.
The connecting part of the monitoring arrangement may also have two further pairs of connecting contacts to which the associated connecting contacts of the device for detecting moisture which are connected to the ends of the portions of the printed conductors can be connected, to make the electrical connection in the connecting part. The end of the portions of the printed conductors may however also be connected together directly at the connecting member of the detecting device.
The connecting part of the monitoring arrangement preferably takes the form of a clamping device for clamping the covering, and in particular the connecting member of the covering. The clamping device preferably has means by which the device for detecting moisture is so aligned and/or fixed in position that the connecting contacts of the device for detecting moisture are situated opposite the corresponding connecting contacts of the connecting part of the monitoring arrangement. These means may take the form of recesses corresponding to the shape of the device for detecting moisture or projections corresponding to the shape of the cut-outs in the device for detecting moisture. The fixing in position may be achieved by positive interengagement, connection by a force or connection by friction. The connecting contacts themselves may even take the form of means for fixing in position. The connecting contacts may for example be spigots which penetrate into the covering.
The arrangement according to the present invention for monitoring a patient access may form a separate unit or may be part of the apparatus by which a liquid is fed to the patient and/or liquid is withdrawn from the patient and may in particular be part of the apparatus for extracorporeal blood treatment. When the monitoring arrangement according to the present invention is part of the blood-treating apparatus, the monitoring arrangement may make use of certain assemblies or components which are present anyway in the blood-treating apparatus.